1. Field of the Invention
This invention relates to a printing paper for making a hard copy of an image picked up by a video camera or a television picture image by thermal transfer of sublimable dyes.
As is known in the art, hard copies by thermal transfer printing are obtained by superposing a dye carrier ribbon having a colorant layer, in which sublimable dyes are contained, on a printing paper and heating the ribbon according to a pattern corresponding to image information, for example, image information picked up by a video camera or television picture image information, causing the sublimable dyes to be transferred on the printing paper. In FIG. 1, there is shown a printer used to obtain a hard copy by thermal transfer printing. The printer has a platen 2 on which a printing paper is wound and which is rotated in the direction arrow (a), and a heating head 4 for pressing a dye carrier ribbon 3 against the platen 2. At the tip of the heating head 4 are arranged heating elements 4a corresponding to the number of picture elements which in turn correspond to one scanning line of, for example, a television picture image.
The dye carrier ribbon 3 sandwiched between the heating head 4 and the printing paper under pressure has a sheet substrate 9 on which there are formed colorant layers of a form corresponding to the frame of a television picture image, which contain the respective sublimable dyes of yellow, magenta, cyan and black in color. In other words, the respective colorant layers including yellow Y, magenta M, cyan C and black B are successively formed in a repeated fashion. In order to permit the respective colors to be detected, detection marks 5Y, 5M, 5C and 5B from which the position of each colorant layer is detected are provided at one side edge of the substrate 9 as shown. Likewise, for detection of a block consisting of the dye portions Y, M, C and B, a block position-detecting mark 6 is provided at the other side edge of the substrate 9.
In case where the ink portion Y is, for example, in pressure contact with the printing paper 1 and the respective head elements 4a of the head 4 are heated in a pattern corresponding to picture elements of one scanning line according to information corresponding to yellow, e.g. a color signal corresponding to yellow of a television picture signal, the sublimable yellow dye in the dye portion Y is thermally transferred to the printing paper according to the heating pattern.
When the platen 2 is intermittently rotated along the arrow (a) every line corresponding to the respective scanning line, information of each line is thermally transferred until the transfer of yellow color corresponding to one frame is carried out during one cycle of rotation of the platen 2. Subsequently, a similar transfer process is conducted with respect to magenta M, followed by repeating the thermal transfer with respect to cyan C and black B. The transferred images of the sublimable dyes of yellow Y, magenta M, cyan C and black B are superposed and thus a color image is developed on the printing paper to obtain a hard copy.
Reference numerals 7 and 8 are, respectively, a light source (e.g. an infrared light emission diode) and a photo detector which constitute a detector means for detecting the marks 5 (5Y, 5M, 5C and 5B) and 6 in order that signals corresponding to the respective color signals in the dye portions Y, M, C and B are supplied to the head elements 4a of the head 4.
A known printing paper used for the above printing operations is, for example, a wood free paper whose surface is coated with a resin coating containing pigments. This type of printing paper is described, for example, in Japanese Laid-open Patent Application Nos. 57-91296, 57-107885 and 58-209596.
The printing paper has an improved color density or dying property and an improved fade resistance, but there is an increasing demand of further improvements of these properties. In addition, the known printing paper is not always satisfactory in preventing sticking between the printing paper and the dye carrier ribbon. More particularly, if sticking takes place, all the ink on the dye carrier ribbon is transferred and deposited on the surface of the printing paper, disenabling one to obtain a print with a clear image.